Seafloor direct push system

Spreader frame keeping slings vertical while lowering seafloor

Seismic pendulum hammer

We have developed a seafloor direct push system enabling us to perform either cone penetrometer or dilatometer with true interval seismic tests from the mudline of a river. The crane operator on the barge lowers this 15 ton thrust capacity equipment to the mudline with a spreader frame as we add push rods and depth reference casing. Our stable platform eliminates the parasitic effects of waves and tides as well as the lack of lateral support for the push rods in the water column. The base for the seafloor resembles a giant plus symbol having outside dimensions of 15.3 feet and applies a low bearing pressure of 145 psf or 6.94 kPa. Essentially, after the seafloor system rests at the mudline, we push the dilatometer or cone penetrometer probe just like we do for land soundings.

Often, rivers have an extremely soft mud layer that the geotechnical engineer needs to evaluate its strength and deformation properties. Drill casing and push rods will often sink into these soft muds under their weight to depths up to 40 feet and CPTU or DMT testing with a drill rig may skip these soils. Our seafloor system simply lowers either the CPTU or DMT probe into these muds at the controlled rate of 2 cm/second as we accurately measure their properties.

We use a 200 pound pendulum hammer to generate high energy shear waves with horizontal particle motion and vertical direction of propagation that we accurately measure with our true interval seismic DMT probe. Our “box lid” seismic plate embeds into the river mudline soils and creates excellent coupling to transfer the shear waves through the soil to our seismic DMT geophones that they accurately measure.